1. Field of the Invention
This invention relates generally to dowel bars used for restricting relative vertical movement between adjacent cast-in-place slabs and more particularly to a dowel bar sleeve system and method adapted to allow relative lateral movement of the slabs along the longitudinal axis of the joint between the slabs and adapted to allow the joint to open and close.
2. Related Art
FIG. 1 is a plan view of adjacent cast-in-place slabs 100-1, 100-2, 100-3, and 100-4 (collectively 100). As is well known in the art, joints 102-1, 102-2, 102-3, and 102-4 (collectively 102) separate slabs 100. Joints 102 are useful for, among other things, reducing failure of slabs 100 in the form of cracking due to expansion and/or contraction of adjacent slabs 100. As is also well known in the art, dowel bars 104-1, 104-2, 104-3, 104-4, 104-5, 104-6, 104-7, and 104-8 (collectively 104) spanning a joint 102 allow the adjacent cast in place slabs to move apart from each other parallel to the dowel bars 104 spanning the joint 102 between the slabs 100. Dowels 104 could have a circular or rectangular cross-section. Dowels 104 are typically used to prevent relative vertical movement between adjacent slabs, which can be visualized as "into or out from the paper" in FIG. 1.
Movement of slabs 100 away from each other along a dowel 102 is commonly referred to as the joint "opening". Similarly, movement of slabs 100 toward each other can be referred to as the joint "closing". For instance, joint 102-1 would open as slab 100-1 moves in the direction indicated by arrow 106 and/or as slab 100-2 moves in the direction indicated by arrow 108. Arrows 106 and 108 point perpendicular to the longitudinal axis of joint 102-1, while arrows 110 and 112 point parallel to the longitudinal axis of joint 102-1.
A significant shortcoming of prior art dowel bars is that they tend to restrict relative lateral movement between adjacent cast-in-place slabs. For instance, dowel bars 104-1 and 104-2 would undesirably restrict slabs 100-1 and 100-2 from moving relative to each other along the longitudinal axis of joint 102-1, which is parallel to arrows 110 and 112. For instance, U.S. Pat. Nos. 5,005,331, 5,216,862, and 5,487,249 issued to Shaw et al., which are incorporated herein by reference, disclose tubular dowel receiving sheaths for use with dowel bars having a circular cross-section. Such dowel bars and receiving sheaths typically do not allow relative lateral movement of adjacent cast-in-place slabs along the longitudinal axis of the joint between the slabs.
This shortcoming has been addressed by U.S. Pat. No. 4,733,513 ('513 patent) issued to Schrader et al., which is incorporated herein by reference. The '513 patent discloses a dowel bar having a rectangular cross-section and resilient facings attached to the sides of the bar. The resilient facings allow for relative lateral movement of adjacent cast-in-place slabs. The '513 patent, however, undesirably requires the resilient facing to be attached to the rectangular dowel bar, which can be costly.
Accordingly, there is a need in the prior art for a less expensive apparatus that prevents relative vertical movement between adjacent cast-in-place slabs, while allowing the joint between the slabs to open and allowing relative lateral movement between the slabs.